This invention relates to establishing a seal between two substrates. When attaching two substrates to each other, it is often important to provide an adhesive or sealant that sufficiently wets-out over the bonding surface, prior to bond formation. The degree of wet-out over the contact surface typically impacts the bond strength. The integrity of the seal can depend upon the proper adhesive strength and the curing properties of the adhesive used in forming the seal. An appropriate surface contact between the adhesive and the substrate will enable a strong seal between the two substrates and thus prevent leakage through the bond line.
The integrity of the seal is particularly important where at least one of the substrates is glass. Many applications exist where it is necessary to secure a glass substrate within a frame such as a metal, plastic or wood frame, which may be painted. For example, a glass windshield or glazing is secured within the metal or plastic frame of a motor vehicle both during vehicle manufacture and during the replacement of damaged windshields on motor vehicles.
Polyurethane pastes are conventionally used to establish a seal between the primed glass and the frame. Such pastes, however, are difficult to apply uniformly and reproducibly. Additionally, such materials involve the undesirable use of wet chemistry, or solvent-based compounds, at the point of application. Another problem is that pushing the glass into the frame causes the paste to flow and squeeze out of the bond line. This creates bond lines of uneven thickness and glass-frame contact points that can act as failure points because any stress applied to the frame is transmitted directly to the glass at these points.
Another problem is encountered in the case of polyurethane sealant pastes that require a relatively long time to cure and build bond strength such as those which are moisture-curable. During this vulnerable curing period, the glass can vibrate within the frame, making the seal and the glass susceptible to damage. Gaps in the seal can form, giving rise to wind noise and compromising seal integrity. The noise associated with the vibrations is also undesirable. Moreover, the reliance on ambient moisture means that the cure process varies depending upon ambient conditions.
Thus, there is a need for a sealant that does not exhibit the above-described problems.